Bimetallic light meter



Nov. 23, 1943. -r 2,334,969

BIMETALLIC LIGHT METER Filed July 1, 1942 llll /7 f; a; I

/6 FIG. 4.

Patented Nov. 23, 1943 UNlTED STATES PATENT OFFICE BClalms.

The invention relates to light meters, and more particularly to a light meter embodying the use of a pair of bimetal strips or coils, one of which is light absorptive and the other not light absorptive, the second coil being principally responsive toheat waves and acting as a correction for the temperature fluctuations of the first coil.

It is well known that bimetallic strips or coils have been used for indicating changes in temperature. In order to make it. possible to use a bimetal coil to measure light it is necessary to compensate for the heat effect on the coil. This is done according to my invention by using a second coil having approximately the same curvature and metal qualities as the first, the second coil being used as the reference or beginning point for the first coil. If both coils are rendered equally responsive to heat waves while only the first is responsive to light waves then the additional curvature of the first coil can be used as a measure of light. This is done by applying a black paint to 'the light absorptive coil, and preferably applying white paint to the compensating coil. It is known that various paints have different capacities for absorption or emission of light and heat waves, and accordingly-various types of paints may be used to affect the sensitivity of the bimetallic coils. A perfect recorder would have equal emission qualities for both paints in the long wave or heat wave zone. The

paint on the first coil should be such as to absorb all of the rays in the short or light wave zone, while the paint of the second coil should be of such character as to absorb none of these rays. While absolute perfection will not be attained in practice,'it is possible to secure very good results by the use of a light, absorptive coil painted black and a compensating coil painted white.

The invention will be more readily understood by reference to the accompanying drawings, in which is set forth by way of illustration an apparatus embodying my inventive thought, although it will be understood that the invention is not limited to the particular details disclosed therein.

larger scale than in Fig. 1; and Fig. 4 is a side elevation of the same.

Referring to the drawing in detail the reference numeral I denotes a bimetallic coil which is painted black and is accordingly relatively light absorptive, and the numeral II denotes a bimetallic compensating coil which is painted white and is accordingly relatively light nonabsorptive. As shown, the bimetallic coils in and I I are so mounted that the white coil I I acts as a reference point for the black'coil I0. As

shown, the inner end of the white coil II is attached to a tube I2 which in turn is secured in the tape! a box I3 housing a suitable clock actuated drum I4 serving as a recording mechanism.

The axis end of the coil II is preferably secured I end of the light absorptive coil In. The inner shaft end of the coil III is connected to a rotatable I8, the other end of which is pointed at I9 andrests upon a suitable bearing 20 on the top of a post 2| extending upwardly from the bottom (2); the Easing1 cr lliousing I3. An upper bearing or e s a t 8 is rovided he the tube .2. I p ar the top of To the lower end of the shaft arm 23 by means of a suitable clamp 24, the other end of which carries a pointer or pen 25 which is adapted to form a suitable graph upon I8 is secured an d the surface of the drum I I as the same is rotated,

and the arm 23 is moved back and forth on rotation of the shaft I8, owing to differences in ex-- pansion between the two bimetal coils I0 and I I due to the fact that one is light absorptive and the other is not. The drum I4 may be of any suitable conventional type rotated continuously through suitable gearing 26 and 21 which may be actuated by clock mechanism or other suitable motive means. The coils I0 and II are preferably housed within a translucent globe 30 which is suitably secured to the top of the casing I3 by clamps 3I. Preferably, openings 32 are provided within the casing I3 so as to allow free circu1a tion between the interior of the lower housing and the interior of the globe 30. Likewise, desirably, a shield 33 is provided between the coils I0 and II, the said shield being secured to the tube I2 by means of a collar or the like 34.

It will be apparent that since the white painted compensating coil I I is as responsive to ordinary black coil l0, both coils will respond alike to temperature changes, and as the axis of the white coil II is stationary the free or axis end of the black coil ID also remains stationary with temperature fluctuations alone. Accordingly, rotations of coil l due to temperature of the environment will be compensated for by' the coil l l.

However, as the coil i0 is black, light waves which are principally in the visible spectrum will be absorbed and this additional energy will cause curvature of the coil l0 and consequent rotation of the shaft l8 to which the inner end of the boil it is attached. This rotation of the shaft [8 is amplified by the arm 23 and is thus transmitted to the pen or other recording means 25 which records the variations in light intensity in the form of graphs upon the surface of the rotating drum Hi.

The particular paints employed upon the coils may be varied as desired, it being understood that the coil I0 will have a paint applied thereto which renders it relatively light absorptive, while the coil II is rendered relatively light nonabsorptive. Absolute perfection cannot be expected, however, and some calibration of the machine will be required. However, the heat or long wave emission values of the two coils should be the same and the light absorption values different. For example, white lead has an absorption and emission value of approximately .95 and black paint (carbon) has an absorption or emission value of approximately .96 in the long or heat waves of the environment. The absorptions for these two paints are .11-.l 8 and .97-.98, respectively, for light or short waves. The coils in and ii are the same general construction except for thickness and width.

The reference coil i i is preferably thicker than the light absorptive coil ID as it is used as a reference or starting point for the latter. This difference is not essential, but it is apparent that the lower coil will be less disturbed by mechanical handling and will support the connecting strip more firmly if it is of more substantial construction. The top coil should not contain much bulk as it should be reasonably sensitive to energy changes due to light absorption and free to respond accordingly.

The connecting strips l5, l8 and I! may consist of two strips of aluminum and a small block of wood bolted together'as indicated. The connecting strip may, however, be made entirely of non-conducting material and in one piece. In such case it may be deflected (or bent) outwardly intermediate its ends so as to provide space for the shield 33, which shield would otherwise have to be notched to accommodate the connecting strips l5, l6 and I1. Shield 33 is composed preferably of aluminum.

A sliding connection at the point of contact between the connecting strip and the upper or light absorptive coil i0 is preferably provided so that the relation between the two coils may be changed. While the coils should have identical curvatures, it is difficult inpractice to find two coils which are exactly alike. A slot at the point of connection will permit such adjustments. If the coils do not react exactly alike there will be a shift in the zero reading of light with temperatur changes.

The use of a frosted globe to enclose the coils I0 and II makes it unnecessary to adjust the machine because of the direction of light. Where room and field heat waves as thelight absorptive the globe is on top of the housing and there are no shadows it serves to integrate the light coming from all directions excepting from below.

The invention ha been described in detail for the purpose of illustration, but it will be obvious that numerous modifications and variations may be resorted to without departing from the spirit of the invention.

I claim:

1. In a light meter, a light absorptive bimetal strip, and a second bimetal strip having a heat responsiveness corresponding to that of the first strip but being relatively non-light-absorptive. one end of the second strip being fixed, and the other end connected to one end of the first strip, whereby the second strip serves as a reference for the first strip, and means including a member connected with the free end of the first strip, for indicating deviations due to light changes.

2, In a light meter, a pair of concentrically mounted bimetallic coils similar as to curvature, material and heat responsiveness, but differing in light absorptivity, the coil having relatively low light absorptivity being mounted with its axis end fixed, means connecting the outer ends of the two coils, and means including a member attached to the axis end of the light absorptive coil, for indicating movement thereof.

3. In a light meter, 8. pair of concentrically mounted bimetallic coils similar as to curvature, material and heat responsiveness, but differing in light absorptivity, the coil having relatively low light absorptivity being mounted with its axisend fixed, means connecting the outer ends of the two coils, means including a member attached to the axis end of the light absorptive coil, for indicating movement thereof, and a shield interposed between the two coils.

4. In a light meter, a pair of concentrically mounted bimetallic coils similar as to curvature, material and heat responsiveness, but differing in light absorptivity, the coil having relatively low light absorptivity being mounted with its axis end fixed, means connecting the outer ends of the two coils, means including a member attached to the axis end of the light absorptive coil, for'indicating movement thereof, and means for adjusting the two coils relative to each other.

5. In a light meter, a pair of concentrically mounted bimetallic coils similar as to curvature, material and heat responsiveness, but differing in light absorptivity, the coil having relatively low light absorptivity being mounted with its axis and fixed, means connecting the outer ends of the two coils, means including a member attached to the axis end of the light absorptive coil, for indicating movement thereof, and a frosted globe enclosing the coils.

6. In a light meter, a light absorptive bimetallic coil, a second bimetallic coil similar in material and curvature to the first coil but differing in light absorptivity, and concentric with the first coil, a fixed upright tube to which the axis end of the second coil is attached, a shaft rotatably mounted within the tube, but having its ends projecting beyond the tube, the axis end of the light absorptive tube being attached to the shaft, means connecting the outer ends of the two coils together, and means including a pointer attached to the central shaft, to indicate movement transmitted thereto by movement of the light absorptive coil caused by variations in light intensity.

- HIRAM F. 'I'HUT. 

